a ae 
Histological Studies in the Artemisia Formation 23 
small bundles. The next or middle row occurs only a little nearer 
the central cavity and is composed of about eighteen bundles. 
Alternating with the members of the second row the innermost 
ring or chain possesses the same structure as the former. The 
individual unit of these two. conspicuous rings is composed usu- 
ally of two, sometimes three or four, large open vessels in the 
xylum or inner portion. Opposite these vessels and separated 
from them by a plate of fibers is a circular or globose mass of 
phloem, mostly sieve tubes. The whole is then surrounded by a 
thick sheath of highly lignified fibers with small cavities. Outside 
the bundle is a sheath of storage cells. In this section, then, we 
have a total of forty-two vascular bundles as against sixteen 
in the meadow form. The woody or the supportive portion of the 
individual bundle is greatly developed here. 
There is considerable doubt as to what ieecoeeeatean should 
be placed upon the above structural phenomena. The relative in- 
crease in photosynthetic tissue and in vascular bundles may be 
developed in response to physiological phenomena. De Bary 
makes the statement that, “The comparison of nearly related spe- 
cies inhabiting the water and the land respectively demonstrates 
among the former a considerable diminution in the development 
of bundles, which may extend to the disappearance of the xylem.” 
This fact has been noted already for a number of species, but in 
none is it so marked as in this species of Juncus. Surely the two 
forms possess the structures necessary to fit each to its particular 
habitat. Perhaps the greater accumulation of chlorenchyma in 
the dry form may: be accounted for by a greater light intensity. 
Although light determinations for the two forms were not made, 
it was very evident that the available insolation for the Juncus in 
the wet meadow was much less than that for the species in the 
Artemisia formation because of the crowding in the former hab- 
itat. It is well known that the stronger light will, to a certain 
degree, accelerate the development of chlorophyll resulting in an 
increase in the number of chloroplasts and ultimately in a greater 
number of cells containing chloroplasts. This condition would 
imply a greater photosynthetic activity which would necessitate 
a much increased supply of carbon dioxide, which would be avail- 
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